title: A test method for quantification of stimulus-induced depression effects on perceptual threshold in epiretinal prosthesis.
abstract: OBJECTIVE
  As part of a clinical trial, an investigational epiretinal implant (IMI Intelligent Medical Implant) was implanted in a retinitis pigmentosa patient. The prosthesis was wirelessly controlled by a visual interface containing a microcamera, providing wireless data and energy transmission. Forty-nine (49) electrodes were used for pattern recognition. This study examined the changes of perceptual thresholds over time and its relation to long-term stimulation. The goal of the study was to introduce stimulus-related depression of perceptual threshold (StirDepth) measurements as a method to gain further insight into the safety profile of electrical stimulation.
  
  
  METHODS
  The perceptual threshold was defined as the level of stimulation intensity at which a phosphene perception with a probability of 50% was detected using the Best-PEST method. StirDepth was measured by comparing the threshold changes immediately before and after a stimulation session of using three active electrodes and one passive electrode, which served as control.
  
  
  RESULTS
  The initial threshold of the day remained stable over the observed period. In StirDepth measurement all thresholds raised significantly after the stimulation sessions. The threshold increase of the active electrodes never exceeded that of the inactive control electrode.
  
  
  CONCLUSIONS
  StirDepth measurement is feasible in epiretinal implants. The prolonged stimulation raised no safety concerns in the patient. The threshold increase of both the active electrodes and the control electrode leads one to hypothesise that cognitive or neurophysiological effects are the cause rather than the desensitizing of the retinal network or incipient retinal damage.
authors.affiliation: Department of Ophthalmology, Medical University Graz, Graz, AustriaDepartment of Ophthalmology, University Medical Center Hamburg-Eppendorf, Hamburg, GermanyIMI Intelligent Medical Implants GmbH, Bonn, Germany.
authors.forename: Michaela
authors.initials: M
authors.lastname: Velikay-Parel
authors.forename: Domagoj
authors.initials: D
authors.lastname: Ivastinovic
authors.forename: Thomas
authors.initials: T
authors.lastname: Georgi
authors.forename: Gisbert
authors.initials: G
authors.lastname: Richard
authors.forename: Ralf
authors.initials: R
authors.lastname: Hornig
mesh_terms: D000368:Aged; D004558:Electric Stimulation; D004567:Electrodes, Implanted; D019773:Epiretinal Membrane / Q000503:physiopathology* / Q000601:surgery; D005260:Female; D006801:Humans; D010364:Pattern Recognition, Visual / Q000502:physiology*; D055351:Retinal Neurons / Q000502:physiology*; D012174:Retinitis Pigmentosa / Q000503:physiopathology* / Q000601:surgery; D012684:Sensory Thresholds / Q000502:physiology*; D057488:Visual Prosthesis
keywords: epiretinal implant; perceptual threshold; retinitis pigmentosa; stimulus-induced neuronal depression